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56 lines
1.4 KiB
C++
56 lines
1.4 KiB
C++
/*
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Copyright (C) 1990 Free Software Foundation
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written by Doug Lea (dl@rocky.oswego.edu)
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This file is part of the GNU C++ Library. This library is free
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software; you can redistribute it and/or modify it under the terms of
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the GNU Library General Public License as published by the Free
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Software Foundation; either version 2 of the License, or (at your
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option) any later version. This library is distributed in the hope
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that it will be useful, but WITHOUT ANY WARRANTY; without even the
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implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
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PURPOSE. See the GNU Library General Public License for more details.
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You should have received a copy of the GNU Library General Public
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License along with this library; if not, write to the Free Software
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Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
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*/
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#ifdef __GNUG__
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#pragma implementation
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#endif
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#include <builtin.h>
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/*
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some useful hash functions
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*/
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unsigned int hashpjw(const char* x) // From Dragon book, p436
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{
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unsigned int h = 0;
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unsigned int g;
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while (*x != 0)
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{
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h = (h << 4) + *x++;
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if ((g = h & 0xf0000000) != 0)
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h = (h ^ (g >> 24)) ^ g;
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}
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return h;
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}
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unsigned int multiplicativehash(int x)
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{
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// uses a const close to golden ratio * pow(2,32)
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return ((unsigned)x) * 2654435767;
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}
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unsigned int foldhash(double x)
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{
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union { unsigned int i[2]; double d; } u;
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u.d = x;
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unsigned int u0 = u.i[0];
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unsigned int u1 = u.i[1];
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return u0 ^ u1;
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}
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